Field of the Invention
The invention relates generally to motorized carts of the type used in industrial material handling, and more particularly to electric drive wheels therefor.
Description of Related Art
Sturdy wheeled carts are commonly used in factories and other industrial settings to transport heavy industrial materials from one location to another. Often, the wheeled cart is pulled by a motorized vehicle (e.g., a forklift, tugger, tractor, etc.), especially when larger distances must be traversed. It is not uncommon to connect multiple carts in series, akin to train cars, so that they can be simultaneously tugged in convoy by the motorized vehicle. When the wheeled cart arrives near its destination, which may for example be a manufacturing machine or a storage area, a worker is often required to manually maneuver the wheeled cart a short distance to locate the cart in an optimal resting position. In these situations, a worker's muscular strength is required to move the cart. Because of the very heavy weights carried by the carts, sometimes more than 6,000 pounds, there has been concern about possible injury to workers and to surrounding objects caused by the manual efforts required. Considering the often very large inertia values, the typically repetitive acts of starting, turning and stopping a heavily-loaded cart can inflict damage to the worker's muscles, joints and/or nerves.
To reduce the potential for worker injuries and collateral property damage, the prior art has suggested with limited success to equip a cart with one or more electric motorized wheels. See for one example U.S. Pat. No. 3,380,546 to Rabjohn which discloses an industrial utility cart designed for both self-propelled and manually maneuvered operation. However, the prior art electric carts have several drawbacks. They are notoriously difficult to operate. They are usually not able to be towed by a motorized vehicle, and if they are towing-enabled it is usually difficult or impossible for a worker to disengage the electric drive wheel(s) for towing. Furthermore, the prior art electric carts must be retired for a period every day to re-charge their batteries. While recharging, the cart is not available for useful service.
There is therefore a need for an improved motorized cart for use in factories and other industrial settings to transport heavy industrial materials from one location to another, that is towable, and that does not require long periods of inactive rest for re-charging.
Moreover, there is a need for an improved motorized drive wheel sub-assembly that can be retro-fitted to an existing wheeled cart, and that is low cost yet robust in performance. And furthermore, there is a need for an improved motorized drive wheel sub-assembly that can be configured to lift its drive wheel above the ground for times when the motorized function is not required.